Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$71.92	9.825%	$78.9861	$78.99	$79.00	$79.00
Purchase #2	$50.31	8.547%	$54.61	$54.61	$54.60	$54.60
Purchase #3	$215.57	13.349%	$244.3464	$244.35	$244.35	$244.30
Purchase #4	$98.56	11.457%	$109.852	$109.85	$109.85	$109.90
Purchase #5	$82.98	4.330%	$86.573	$86.57	$86.55	$86.60
Purchase #6	$30.29	13.474%	$34.3713	$34.37	$34.35	$34.40
Purchase #7	$169.65	11.325%	$188.8629	$188.86	$188.85	$188.90
7 purchase totals =	$719.28		$797.6017	$797.60	$797.55	$797.70